Rotatable attenuator for wave guides



July 15, 1952 BOWEN 2,603,710

ROTATABLE ATTENUATOR FOR WAVE GUIDES Filed Dec. 11, 1946 FIG I CONDUCTIVE .s'EPTUM Gums C CONDUCT I YE SEPTUH CONDUCT/V5 sEPruM I AT TENUA TOR our ur t1 our ur ournur I 0F k" 0F "0" or "c" E FIG. 3

JOINT INVENTOR A. E. BOWEN kid. 4

ATTOZNEY t diagram:

Patented July 15, 1952 urtn STATES "PATENT ROTATABLE A'r'rrmoa'rort ron wfiyh comes arn mn nowe Fair H v n;

-"Bell-Telephone-Laboratories;I

-=0rk, N. .,-a corporation of-New'ZYork I :3 7 7 Application pecemher 11,1946, Serial No. 715,589 1 Claim. (oIJi V'sLZQQ This invention relates to variable waveguide attenuators.

;An object of the invention is to vary the attenuation of. electromagnetic Waves in a wave "guide without changing their polarization.

Another object is to continuously vary the attenuation in a waveguide by rotation without ronto'nriitantly-*settin g up undesirable reflections.

' Ahother pbj'ect the invention-is'tocontinuously vary the attenuation'of-a wave without concomitantly changing" the direction of its polarization vector, by continually suppressing quadrature cross components developed during the attenuation. .1

1 -fmnothriiobjectiof:the. 7

atei waves.iiiniaccoifdance with a trigonometric i iu'nction' of 'an 'angleiof rotation.

@mxiotherobject of the-invention is to attenuate waveszpropa'gate'd bilaterally; i. e., in. two oppo- -rsite directiens through a wave guide without --iehanging their direction i polarization.

:A featureof the inveritionis asrotatable attenuator for wave guides comprising a rotatable "'iwa've: guide section connected intermediate to tworistationary guide sections, the 1 rotatable section beingiprovided'l with f a diametral attenuating-plate extending longitudinally, thereof, while ,rthe r-stationary sections are each provided with cross rcomponentsuppressors;

w :1 represents a rotatable attenuator in aceordancerwith the invention.

. -Fig. 2.:is:=an explanatory electric force vector --.-Flg.t3 :illustrates a modification of the-attenuator.

r :Wave guide attenuators have heretofore-Been disclosed, E101 example, in the United states .Patent 2-, l=97,1Z2, issued April 16, 1940, to A; E. Bowen, in the United states Patent 2,197,123, issuedv-April 16, -1940,-to A. P. King, and ihthe United-states Patent 2,151,157, :i's'sued March 19-39, to s. A-'.:ischelkunofi.

Dhe .objectmf suchfattenuators in genera'liis :to attenuatedielectrically guided waves propagated-within metallic pipe 'g'uides without simulrtaneously generating spurious refle tions:

For morep'reeise control of the'prdpagation of waves in hollow pipe wave guides or similar systems, it is desirableto attenuate linearly polarized electromagnetic waves without afiecting or changing the direction of polarization. In accordance with an embodiment of the invention, attenuation without change of polarization is achieved by means of "a rotatable z'it't'e' i'uator,

wherein cross moraine-hen wave components deventi-on iseto attenu- :veloped: the 'bilate Y rguishe d or otherwise suppressed;

ralv or '5unilaterak-tprogress through the; attenuator are absorbejdextin- -In; accordance with an embodiment: invention, sucha rotatable "attenuator :maycompri se ---three tandem wave-guide isections'jA, 3, 0, the intermediate one B 'beingrotatably con- ,nected;to the stationary sections, -A an d;;C, respectively. The guide section B is provided with 'a .;diarnetral and longitudinallyextending -;att, nuatin pl e; h vi im dance matchin terminations of notched or tapered dorm; R0-

tation of the intermediate guide section B through an angle l9- will-produce an attenuation equal to cos 0 in the amplitude of a linearly polarized ,input wave Cross components or quadrature" 'polarizations are suppressed Yin ,the

' ware-guidese tions 'A, o. 7 Intermediate section B is rotatably coupled to the 313321710 extend ng longitudinally there fstationaryfsections' A 'andjC by vlossy plates {backed iipwithjrefie'ctingmetallic septa;

'Refrring'to'Figg 1, there hown tw -wfay or pattern attenuator comprising fcylindrical end s'ectio'ns' A and o by rotatable pi e} a ings illustrated in Fig. 1.

The rotatable guide section 13 consists of-a short length of cylindrical pipe rovidedvwith a H a, .ndfp three-parts z, 3, 4. Parts 3,F4*m yea 51+; ion

- 'pIa'te'sof tne typ 'dis'eios eq ih jtiie nit ds tee attenuation.

patent apart anther -A. E. *Bowen Se 1 No. "4863013, filed -7, 194:3, *now'raten no. -2,600,466,--' 6'r'the United "States giater' 'tjappi or w. Hewitt, Jr.)'Serial fiQLBSLOltO, filed August 24, l9 l4 preferably providing mo'r -10 decibels pr jattenuati g rhemeiab p 3', 4 are provide either with termina'r iinpdance matching-, notchedportions;

1 rain "piat gie ter than.

the-ab orp'tion plates}, 4 for more efiectiye 53'. Pid eq'i' fis A tea- .t .iiso aarit e et @ic imarica wave guide having a conductive septum 5 in- The s'tatio' it is apparent that r tegrally associated with an absorption plate 6, the unit extending longitudinally thereof ina diametral plane. p

Initially the guide sections A, B, Care lined up so that the plates I and 6, 6' are coplanar and :0, whereby both the attenuation of linearly polarized waves transmitted 'therethroug'h is zero, and the direction of polarization is unaltered.

However, when intermediate guide section B is rotated through an angle 0 and the attenuating plate I is inclined 0 to the fixed, common plane 6-6, an .input polarized wave entering section A perpendicular to conductive septum will emerge from section C with'its amplitude attenuated proportional to cos 0 butwith its polarization direction unchangedas will be ently explained in greater detail. v

In actual operation (see' the vector diagramof Fig. 2) suppose an input wave E, polarized perpendicular to the plane of conductive septum 5,

.- enters the attenuator (A, B, C) at the left. Since the septum 5 is perpendicular to E, the wave will emerge from section A unchanged and be incident on the intermediate guide section B. I-Iere E may be resolved into two components in space quadrature, E11, parallel to attenuating plate 1,

and E1, perpendicular thereto. In the passage through section B, the parallel component En.

where a (expressed in decibels) is defined, in general, equal to The values, oft vs. fi in a rotatable attenuator pres- A, B, C-maybetabulated'as follows:

7 v The attenuation at 0:190 degrees dependsgon is fully absorbed by attenuating plate lpwhile the perpendicular component E1 passes freely thereover and into-guide 'section C. FroinFig. 2,,

1 The represented by tionaryend section 0, is resolvable againi'nto two quadrature'components with respectitoithe plane 5'+6.'. Thekcomponent paralleltd septum 6 'willbe transmitted into the absorption plate 6 7 From Fig. 2C,.it..is ap parentthat I E'= E1'cos 0;}; cos a 7, V

In the resolution of vectors in guide sections-B and C as described aboveytheparallel components encounter no discontinuities as they: pass into allthe absorption plates'because of theimpedance matching terminals thereon. Undesirable reflected waves are therefore not generated "by the parallel components. Likewise, the "quadrature components being unaifected by: the per- 'pendicular disposition of the absorption plates thereto suiTer no reflections. Thereby, thewave in its progress through the attenuator encounters 'the same characteristic impedance irrespective of the angle 0 through which section B is rotated and attenuation is achieved without reflection for both directions of transmission. Therefore in Q this system, an impedance match once establishedis maintained .unchangedlthroughout all 1 angular displacements of the absorption plates,

' or expressed slightly difierently, the impedance match is maintained whatever the attenuation introduced may be. I Y

Comparing theinput wave vector E and output vector E, it is apparent that the polarization. directions are alike, but the emergent vectors is relatively reduced in amplitude, proportional tofl 005 19. Accordingly, the rotationof section B a through an angle 9, will produce attenuation proporti-onal to cos 0, without change of polarization I and dissipated therein, whereasthe perpendicularcomponentE (FigPZC) will pass.,freely thereoyer. and emerge.

the length ofthe conductive septum 2,. preferably should be greater than which where A; is the wavelength in theguide. 35

The specific construction of absorptionplate l as disclosed in Fig. lyyields: a higher' ;attenuation in a smaller space than heretoioreLw-The reflecting action of septum 2, on the component parallel theretocauses the latter .to' sufieradditional attenuation in absorptio'n'plate 3.": Without the inclusion of septum'Z, longerattenuatr ing plates in section B wouldbe required to-provide suflicient attenuation. I i r i Likewise, the conductive septa 5'5 by reflecting the quadrature components'back into therespective absorption plates 66, :renderthesuppression of cross components 'inore' effective.

It should be noted with respect to two-way transmission that sections B andC are effective in attenuating waves traveling from'left to right,

and section A further suppresses any cross components reversely-directed. Correspondingly, a wave transmission directed from right to' left, is attenuated in sections A, B,- while reflectedcross components are extinguished by section C. 1 r The embodiment illustrated in Fig. 3 is a modification of the cos 0 attenuator illustrated in Fig. l, utilizing rectangular guide sections for cross component suppression." a

The stationary sections A and C, Fig. 3, are each provided with an end, rectangularwave guide portion 26, so' dimensioned and proportioned as to only transmit waves of one polarization, namely, waves polarized vertically and parallel to the small side b. -The cross-sectional dimensions a, b ofthe rectangular waveguide'26 where M. is the wavelength in air. 75. p

A circular pipe guide portion 27, integral with rectangular guide 26, contains therein in absorp-' impedance matching terminal 28 at the end thereof facing section B. The rectangular guide 26 is connected to the circular pipe 21 by an impedance matching tapered transformer portion 28 whereby a gradual transition from rectangular to circular cross-section is produced, as shown in Fig. 3. In order to further compensate for residual impedance discontinuities between circular pipe 21 and rectangular pipe 26, a variable reactance screw S1 is provided in the latter.

The rotatable guide section B consists of a short length of cylindrical wave guide 29 provided with a diametral attenuating plate 21, extending longitudinally thereof and provided with impedance matching terminations 22. Rotatable joints are provided between rotatable section B and stationary sections A, C at the respective ends thereof as indicated in Fig. 3. Rotary motion through 90 degrees may be imparted to pipe 29 by milled ring 23, having screws I4 movable in slots 15.

The mode of operation of the embodiment shown in Fig. 3 is essentially similar to that described in connection with Fig. I. The rectangular guide 26 passes the incident wave polarized parallel to the dominant E vector and suppresses cross components, parallel to a, the long side of the rectangle analogously to the septa 5-5' of Fig. 1. A rectangular guide dimensioned as above will support the propagation of one polarization parallel to b and cut off a quadrature polarization parallel to a.

The attenuator A, B, C of Fig. 3 may be inserted in a two-Way transmission system and will operate in a manner similar to that previously described in connection with Fig. 1.

In both forms (Fig. 1 and Fig. 3), impedance matching at various sections of the attenuator A, B, C is provided by the notched terminal construction to prevent disturbing reflections being set up. Attenuation is achieved without alter- 6 ing the polarization vector and without reflection.

Although the attenuators have been described particularly in connection with wave guide transmission, it should be apparent to those skilled in the art that they may be applied in concentric line systems or in microwave radio relay link systems.

What is claimed is:

An attenuator for linearly polarized input microwaves comprising a plurality of axially aligned wave-guide sections having dissipative plates therein, said plates adapted to be aligned in a longitudinal plane perpendicular to said linear polarization to provide a zero attenuation,

and means for rotating one of said plates with respect to said longitudinal plane, whereby the attenuation is a function of the angle of rotation, and means for maintaining the polarization of the output waves unchanged with respect to the input polarization.

ARNOLD E. BOWEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,088,749 King Aug. 3, 1937 9 2,129,712 Southworth Sept. 13, 1938 2,197,122 Bowen Ap-r. 16,. 1940 2,207,845 Wolff July 16, 1940 2,257,783 Bowen Oct. 7, 1941 2,407,267 Ginzton Sept. 10, 1946 2,411,534 Fox -2 Nov. 26, 1946 2,423,130 Tyrrell July 1, 1947 2,423,383 Hershberger July 1, 1947 2,425,345 Ring Aug. 12, 1947 2,427,100 Kihn Sept. 9, 1947 2,433,368 Johnson Dec. 30, 1947 2,438,119 Fox Mar. 23, 1948 2,441,598 Robertson May 18, 1948 2,540,839 Southworth Feb. 6, 1951 OTHER REFERENCES Proceedings of the I. R. E., October 1946, page 783. 

